The present invention relates to a secondary battery using a nonaqueous electrolyte, and more particularly to a nonaqueous electrolyte secondary battery capable of charge and discharge at a high current density.
A lithium ion secondary battery is a typical one of nonaqueous electrolyte secondary batteries. The lithium ion secondary battery uses a negative electrode and a positive electrode, wherein the negative electrode may be doped and de-doped with lithium, and the positive electrode contains a transition metal oxide. The negative electrode is shaped in sheet. The sheet-shaped negative electrode comprises a sheet-shaped negative electrode collector applied with a negative electrode active material.
The positive electrode is shaped in sheet. The sheet-shaped positive electrode comprises a sheet-shaped positive electrode collector applied with a positive electrode active material. The lithium ion secondary battery has a lamination structure of the negative and positive electrodes which are separated through a separator. The lamination structure may be coated with a packaging material. Alternatively, the lamination structure may be rolled to form a cylindrically shaped roll structure which is contained in a battery case.
The later one having the cylindrically shaped roll structure contained in a battery case is particularly superior in sealing characteristic. The cylinder shape allows a uniform battery reaction over position of the lamination structure. The nonaqueous electrolyte secondary battery is used for obtaining a large current. The cylinder shape is important for the nonaqueous electrolyte secondary battery. The cylindrically shaped nonaqueous electrolyte secondary battery is expected as a large battery for driving an electric car or an electric auxiliary bicycle.
FIG. 1 is a fragmentary cross sectional elevation view illustrative of a conventional cylindrically shaped nonaqueous electrolyte secondary battery.
A battery 51 has a battery case 52 which accommodates a battery element 56 which comprises a roll structure of laminations of sheet-shaped negative and positive electrodes 53 and 54 separated by a separator 55, wherein the negative electrode 53 comprises a negative electrode collector provided with a negative electrode active material, whilst the positive electrode 54 comprises a positive electrode collector provided with a positive electrode active material. The separator 55 is wider than the negative and positive electrodes 53 and 54. The battery case 52 is cylindrically shaped to accommodate the cylindrically shaped roll structure of the laminations. The lamination structure is rolled around a center axis of the cylinder A width direction of the separator 55 and the negative and positive electrodes 53 and 54 corresponds to the direction of the center axis of the cylinder. The separator 55 is wider than the negative and positive electrodes 53 and 54, so that opposite sides of the cylindrically shaped battery element 56 comprise side portions of the separator 55, wherein the side portions of the separator 55 project from the side portions of the negative and positive electrodes 53 and 54. The battery case 52 may serve as a negative electrode terminal. In this case, the sheet shaped negative electrode is attached with a stripe-shaped negative electrode lead 57. This stripe-shaped negative electrode lead 57 is welded to an inner wall of the battery case 52. A positive electrode lead 58 is attached to a battery header 59. The battery header 59 serves as a positive electrode terminal. The battery header 59 has a pressure release valve which releases an internal pressure of the battery if the internal pressure is excessively increased.
In the above battery, the stripe-shaped electrode leads are attached to the collectors. If the large current is fetched from the battery, a current distribution is different between a position adjacent to an attachment position of the electrode lead and a position far from the electrode lead. In Japanese laid-open patent publication No. 7-192717, it is disclosed that in order to solve the above problem, the electrode lead is used which has a large sectioned area. Also, it is disclosed that a large number of the electrode leads are attached, thereby making an attachment portion of the electrode lead thick, resulting in a non-uniform distance between the positive and negative electrodes in the form of the roll structure. This provide undesired influence to the characteristics of the battery,
In Japanese laid-open patent publication No. 6-36756, it is disclosed that in order to fetch the current uniformly over the positions of the roll structure, a nickel-cadmium battery of a sintered type is provided wherein a large number of plate-shaped collectors are connected to a sealing cap provided in the battery case, and a metal spring is provided to contact with the sealing cap and the collectors to form a conduction path between the sealing cap and the collectors.
In Japanese laid-open utility model publication No. 5-45898, it is disclosed that a metal foam is provided to form a current divided path.
The formation of the current divided path provides an effect of reduction in IR loss as compared to when only the electrode leads are provided, but this effect is not so different from when a large number of the electrode leads is provided. If this technique is applied to the nonaqueous electrolyte secondary battery, then problems are raised with a possible breaking of connecting part of the electrode leads due to vibration of the battery.
In order to connect the electrode leads to the positive electrode collector and the negative electrode collector, it is necessary that a positive electrode active material and a negative electrode active material are applied on the positive electrode collector and the negative electrode collector before the metal strips are bonded by a welding method to active-material-stripped faces of the connecting parts of the electrode leads. In order to reduce the IR loss, a large number of the electrode leads are plugged to take a long time for connecting the electrode leads. This means that the fabrication processes are complicated.
In Japanese laid-open patent publication No. 9-306465, there is disclosed a nickel-hydrogen secondary battery using a winding type battery element, wherein the number of the connecting parts, per one turn or one round, of the electrode plates connected to the collector terminal is increased from an innermost position to an outermost position so as to improve uniformity of the current fetch from the roll body. It is, however, necessary that the electrode plates are bonded by a welding method to the collector terminal. This bonding process makes long the necessary time for the fabrication of the battery.
In the above circumstances, it had been required to develop a novel nonaqueous electrolyte secondary battery free from the above problem.
Accordingly, it is an object of the present invention to provide a novel nonaqueous electrolyte secondary battery free from the above problems.
It is a further object of the present invention to provide a novel nonaqueous electrolyte secondary battery which is capable of reducing an IR loss even in a highly efficient discharge process.
It is a still further object of the present invention to provide a novel nonaqueous electrolyte secondary battery preventing a conductive connection between a battery element and a battery case from being broken due to vibration of the battery.
It is yet a further object of the present invention to provide a novel nonaqueous electrolyte secondary battery having a highly reliability.
It is yet a further object of the present invention to provide a novel nonaqueous electrolyte secondary battery which allows simplifying the fabrication processes.
It is yet a further object of the present invention to provide a novel nonaqueous electrolyte secondary battery which allows shortening the necessary time for the fabrication processes.
The present invention provides a nonaqueous electrolyte secondary battery comprising: a battery case; a battery element accommodated in the battery case, the battery element comprising laminations of a first polarity type electrode, a second polarity type electrode and a separator sandwiched between the first polarity type electrode and the second polarity type electrode, the first polarity type electrode comprising a first polarity type collector which is provided with at least a first polarity type electrode active material layer except for a first side region extending along one side of the first polarity type collector, and the second polarity type electrode comprising a second polarity type collector which is provided with at least a second polarity type electrode active material layer except for a second side region extending along one side of the second polarity type collector, the first side region of the first polarity type collector projecting from first side edge of the separator and the second side region of the second polarity type collector projecting from second side edge of the separator, so that the battery element has a bottom portion which comprises the first side region of the first polarity type collector and a top portion which comprises the second side region of the second polarity type collector; a bottom conductive elastic material on a bottom of the battery case, and the bottom conductive elastic material being in contact with a substantially entire part of the bottom portion of the battery element; and a top conductive elastic material on a top of the battery case, and the top conductive elastic material being in contact with a substantially entire part of the top portion of the battery element.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.